This invention relates to apparatus used to establish an extracorporeal blood circuit used, for example, to perform hemodialysis. It also relates to monitoring the blood pressure in such a blood circuit and more particularly to noninvasive blood pressure monitors.
Hemodialysis apparatus for artificial kidneys generally comprises a supported, semipermeable membrane made of a cellophane-type material, positioned in a casing to provide a blood flow path along one side of the membrane and a dialysis solution flow path along the other side, for diffusion exchange across the membrane between the blood and the dialysis solution without the direct intermixing of the two liquids.
In the actual hemodialysis process, a considerable number of processing steps are required during the operation of bringing the blood to the hemodialyzer, and withdrawing it from the hemodialyzer for return to the patient. In the presently conventional arterial and venous sets which are used to withdraw blood from a patient, convey it to the dialyzer, and return it again to the patient, bubble traps, filters, sterile access sites for injection needles, and access sites for pressure monitor equipment may all be included on the sets, which primarily comprise flexible, blood compatible plastic tubing. Accordingly, in the present technology of dialysis, two different and separate long, tubular sets are utilized, the arterial set upstream from the dialyzer in terms of blood flow, and the venous set downstream from the dialyzer.
Hence, to set up a dialysis procedure, a dialyzer must be selected, and the nurse must also separately obtain an arterial set and a venous set. The packaging of all of these devices must be opened, and the devices respectively must be connected and assembled together, with other auxiliary equipment being also added to the system. This requires the services of a highly trained technician, who must make a considerable number of connections between the sets and the dialyzer, flawlessly and without error.
In accordance with this invention, a one-piece hydraulic circuit is provided to replace many of the functions of the arterial inlet and outlet sets, and auxiliary equipment. The one-piece hydraulic circuit may be connected to the dialyzer itself at the time of manufacture, if desired. The setup of the dialysis system prior to use is thus greatly simplified, eliminating many of the connections which must be made by the technician at the site of use, which, in turn, reduces the possibility of error, and contamination of the system during the assembly and connection process. Furthermore, the system of this invention is compact and simplified, saving a considerable amount of valuable space around the bed during the dialysis procedure.
Additionally, the blood pressure within the extracorporeal blood circuit is continuously monitored so that adjustments to the system may be made if the pressure falls outside prescribed limits during treatment. It is preferred that the pressure monitoring be accomplished without the pressure sensing device contacting the blood within the extracorporeal blood circuit, thus preventing contamination of the blood as well as preserving the integrity of the pressure sensing device for subsequent use.
The blood pressure is typically monitored at a bubble trapping chamber normally used in an extracorporeal blood circuit. Also used are pressure monitors of the noninvasive type such as disclosed in U.S. Pat. Nos. 3,713,341 and 3,841,157 and 4,077,882. These pressure monitors employ a pressure transfer element which compresses or expands a fixed volume of a compressible fluid such as air in response to pressure changes within a closed chamber. Calibration of such a monitoring device is therefore required to compensate for the compressibility of the fluid and the amount of pressure needed to overcome the inertia of the pressure transfer element itself.